1. Dear Drugs-Forum readers: We are a small non-profit that runs one of the most read drug information & addiction help websites in the world. We serve over 4 million readers per month, and have costs like all popular websites: servers, hosting, licenses and software. To protect our independence we do not run ads. We take no government funds. We run on donations which average $25. If everyone reading this would donate $5 then this fund raiser would be done in an hour. If Drugs-Forum is useful to you, take one minute to keep it online another year by donating whatever you can today. Donations are currently not sufficient to pay our bills and keep the site up. Your help is most welcome. Thank you.
    PLEASE HELP

Modification of morphine tolerance by behavioral variables

Modification of morphine tolerance by behavioral variables

  1. Anonymous
    C A Sannerud and A M Young
    J Pharmacol Exp Ther. 1986 Apr;237(1):75-81.

    Abstract

    These experiments assessed whether the opportunity to perform a target operant in the presence of morphine would alter the development of behavioral tolerance. Morphine tolerance was assessed in rats responding under a fixed-ratio 30 schedule of food delivery. Separate groups of rats were administered 10 mg/kg of morphine either pre- or postsession for 9 weeks. The degree of drug tolerance was assessed by determining cumulative dose-response functions for morphine before, during and after chronic administration. Three to 4-fold tolerance to the rate-decreasing effects of morphine developed in rats receiving morphine presession, whereas no tolerance developed in rats receiving an equal dose of morphine postsession. Morphine sensitivity returned to initial values 4 weeks after termination of chronic administration. Eight weeks after termination of chronic administration, the drug-daily session relationship was reversed and the rats were re-exposed to 10 mg/kg of morphine for 9 additional weeks. There were fewer differences between groups receiving morphine pre- or postsession during this second chronic administration phase. During chronic administration of morphine, the dose of naloxone required to suppress response rates decreased 100-fold in rats receiving morphine presession, but only 10-fold in rats receiving morphine postsession. In contrast, chronic administration of morphine did not alter the rate-decreasing effects of the nonopioids d-amphetamine, ketamine or pentobarbital. These experiments suggest that reinforcement of an operant response in the presence of morphine promoted the development of pharmacologically specific behavioral tolerance to morphine.